One of the main problems faced by today's spacecrafts and other hypersonic vehicles is the great temperatures that must be withstood by the structures of those vehicles. The high temperature conditions faced by vehicles such as the Space Shuttle, particularly during re-entry, are accompanied by extreme physical forces, such as hot gas impingement and both operational and acoustic vibrations as well.
At present, one of the major areas of concern with regard to heat insulation of the Space Shuttle is in the Main Engine (SSME) nozzle section which is exposed to extremely high temperature and other significant physical forces primarily during re-entry into Earth's atmosphere. These engine nozzles must be well insulated in order to remain below specific temperature limits so as to preserve the heat treated structural properties. During the course of a mission, the nozzles will experience significant flexure from start-up transients, change of shape due to pressurization to steady state values, change of size when chilled to operational temperatures, and high acoustic, structural dynamic and aerodynamic loading pressures. These factors rule out use of high temperature ceramics because of their generally brittle nature.
On previous shuttle missions, nozzle insulation has been provided by a barrier consisting of a NiCr screen containment skin, NiCr foil convection shield and a sintered NiCr batting. Although this insulation material can give high temperature protection (about 2550.degree. F.), date from the recent missions indicated that heat loads of up to about 27.72 BTU/ft.sup.2 -sec will be faced by these nozzles, and the current insulation can withstand only about 22.0 BTU/ft.sup.2 -sec. Clearly, a material with greater insulation properties is needed for the SSME nozzles.
There are other known methods and materials for enabling space structures to withstand the harsh high temperature environment faced during re-entry. Many examples of such insulation materials are disclosed in the patent art, including those described in U.S. Pat. Nos. 4,581,285; 4,344,591; 4,198,454; 3,799,056; 3,715,265; and 3,203,849. Generally, previously known solutions for this problem either use ablative materials or positive cooling via a heat exchanger. Unfortunately, none of these previously used materials have all of the characteristics necessary to be successfully used as SSME nozzle insulation; Among these required characteristics are flexibility (for nozzle start transients), oxidation resistance (when exposed to high temperature oxygen atmosphere), high emissivity (required for radiation cooling), and vibration resistance (needed for acoustic and operational vibration). In addition, the nozzle insulation material must also be lightweight, as well as easily and securely attachable to the SSME nozzles. A material having all these features would be highly desirable for use on upcoming shuttle missions.